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Ecological Risk and the Evolution of Great Ape Life Histories

Ecological Risk and the Evolution of Great Ape Life Histories

(p.3) 1 Ecological Risk and the Evolution of Great Ape Life Histories
Chimpanzees in Context
Cheryl D. KnottFaye S. Harwell
University of Chicago Press

Primates are characterized as having slow life histories. Great apes exemplify this with relatively longer juvenile periods, later ages at first birth, long interbirth intervals, longer lifespans, and fewer offspring. However, there are significant differences in life history parameters amongst the great apes that have not been adequately explained. This chapter compares infant mortality, age at menarche, age at first reproduction, interbirth interval, age at last birth, and lifespan of the great apes at different long-term field sites and in captivity. These traits display a continuum, with gorillas having the fastest life history, followed by the two Pan species, then orangutans. It is proposed that relative ecological risk, at the genus level, best accounts for these differences. The data presented in this chapter demonstrate that orangutans experience the highest variability in nutritional intake and gorillas the least. Increased ecological risk, specifically starvation, is predicted to result in the selection for a slower life history pattern. A slower life history overall mitigates the effects of ecological risk by distributing energetic demands over longer time periods. Species with the slowest life history, and the greatest ecological risk, also show the greatest phenotypic plasticity when in captivity, where there is lowered ecological risk.

Keywords:   life history, ecological risk aversion, development, reproduction, great apes, interbirth interval, menarche

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